Carbonates and Evaporites
Volume 17, Number 1, 2002, June
abstracts
FACIES, MICROFACIES, AND DIAGENESIS OF LATE CALLOVIAN-EARLY OXFORDIAN CARBONATES (LA MANGA FORMATION) IN THE WEST CENTRAL ARGENTINEAN HIGH ANDES
Gabriela L. Lo Forte and Ricardo M. Palma
Universidad de Buenos Aires-CONICET. Departmento de Cs. Geológicas, Pabellón II. Cuidad Universitaria. (1428). Buenos Aires. Argentina;
[email protected], [email protected]
ABSTRACT: At 32 40' south latitude the Andean orogen shows a typical thin-skiinned fold and thrust belt that exposes the Mesozoic back-arc basin fill. The late Callovian - early Oxfordian limestones of the La Manga Formation were studied based on lithofacies, microfacies, and diagenetic processes in order to interpret the paleoenvironment depositional setting. Five lithofacies can be recognized within the La Manga Formation: (A) stromatolite mudstone, (B) massive and laminated carbonate mudstone, (C) massive wackestone, (D) coralline floatstone, and (E) oolitic-skeletal packstone-grainstone. The vertical succession reveals six closely related microfacies grouped as follows: (1) stromatolite mudstone, (2) peloidal wackestone, (3) bioclastic peloidal wackestone, (4) oolitic bioclastic packstone, (5) coral skeletal floatstone, and (6) oolitic-intraclastic grainstone.
Diagenetic events, listed in sequence, include: 1) dissolution of high-Mg calcite and aragonite shells; 2) compaction; 3) pore filling; and 4) pressure-solution. Three types of cement, isopachous, granular calcite and sytaxial overgrowth, were identified. Based on CL petrography the cement sequence changes from non-luminescent to brightly luminescent, suggesting variations within the pore fluid system. Paleotemperature during deposition is estimated at 26C according to stable isotope analyses on oyster shells.
Lithofacies and microfacies data suggest that an intertidal-lower supratidal environment (lithofacies A and microfacies 1) was followed by a deepening succession (lithofacies B, C, and microfacies 2, 3), followed by a shallowing upward succession (lithofacies D, E, and microfacies 2,3), followed by a shallowing upward succession (lithofacies D, E, and microfacies 4, 5, 6). This facies assemblage is interpreted as part of a transgressive system tract and a high-stand succession. The sequence represents an upward-coarsening deposit on a shallow carbonate platform.
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IDENTIFICATION OF CLASTIC-EVAPORITE UNITS IN ABAR-KUH PLAYA (CENTRAL IRAN) BY PROCESSING OF SATELLITE DIGITAL DATA
Mahmoud Khalili & Homayon Safaei
Department of Geology, University of Isfahan, 81744 Isfahan, Iran
ABSTRACT: The Abar-Kuh playa, with more than 1750 km2, is one of the central Iranian playas. Several different clastic-evaporite units have been identified on the basis of field observations, mineralogy and geochemistry as well as landsat TM data. Based on these data, for the first time, a number of major faults have been recognized. These faults have certainly had profound effects on the extension of sedimentary-evaporites units in the study area. Also, the borate mineral of ulexite was found in evaporite zone, which can be probably a good base for the future borate discoveries in the study area.
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A DEVONIAN (GIVETIAN) FORE-REEF SLOPE SEQUENCE AT LIANGSHUIJING AND IMPLICATION FOR DEVONIAN PLATFORM-TO-DEPRESSION DEVELOPMENT IN GUILIN, SOUTH CHINA
Jian-wei Shen
Department of Earth Sciences, University of Queensland, QLD 4072, Australia
ABSTRACT: Three Bahama-like carbonate platforms-the Guilin, Yangshuo and Yanshan-occurred in Guilin and the surrounding regions during Middle and Late Devonian, which, at a broad scale, are part of an extensive carbonate platform (Xiangzhou carbonate platform) facies in South China. The intraplatform depression facies, a unique characteristic of the Chinese Devonian depositional sequence, separates Bahama-like (platform-to-depression) carbonate subplatforms. Intraplatform depressions resulted from syndepositional faulting that cut the basement of carbonate subplatforms and affected further platform development. The Liangshuijing section, located between the Guilin platform in the north and the Yangshuo platform in the south, is representative of the fore-reef slope facies neighboring an intraplatform depression. The south edge of the fore-reef slope lies adjacent to the Yangshuo reef carbonate platform, and the north edge graded into the Yangdi pelagic depression facies. A detailed sedimentary and microfacies analysis work done in this study at the Liangshuijing section shows a distinct vertical facies change from back-reef, restricted platform, hemipelagic, to fore-reef slope facies, differing from either shallow-water benthic facies or typical pelagic facies. Various benthic and pelagic lithofacies and their associations have been recognized in the Liangshuijing section, including dolomitic rudstone, gastropod wackestone, Amphipora floatstone, tentaculitoid wackestone, stromatolite and oncoid limestone, Amphipora grainstone, grain flows, laminated limestone, flat-pebble and brachiopod floatstone, and carbonate turbidites. Eight types of sedimentary cycles composed of two or three lithofacies have been distinguished, which are able to indicate environment changes. Stromatolites, oncoids, grain flows, carbonate turbidites, and tentaculitoid limestones characterize the slope and intraplatform depression lithofacies. Analysis of the vertical sedimentary cycles in the Liangshuijinag section and the lateral stratigraphic equivalents suggest the differing facies patterns occurred at the middle Varcus Zone (Givetian) of Middle Devonian, coeval with the development of fore-reef slope facies in the Guilin area in response to syndepositional faulting.
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GEOCHEMICAL STUDY OF LIME-MUD BORINGS AND ASSOCIATED CORAL-REEF LIMESTONES IN THE INTERTIDAL FLAT OF KONDOI BEACH, TAKETOMI ISLAND, OKINAWA, JAPAN
Satoshi Yamamoto
Laboratory of Oceanography, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0129, Japan; [email protected];
Fax: 098-895-8552
ABSTRACT: Various types of numerous lime-mud borings have been discovered in the intertidal limestone and coral (Acropora) framestone at Kondoi Beach of Taketomi Island, Okinawa, Japan. Lime-mud borings may be formed by a mechanism similar to that for the micrite envelopes in molluscan shells and other carbonates. The lime-mud borings and surrounding limestone/coral framestone were pairedwisely sampled and analyzed geochemically. The lime-mud borings show a rather uniform mineralogical composition (about 80% high-Mg calcite (HMC), 10% aragonite, and 10% low-Mg calcite (LMC)), whereas the surrounding limestone appears HMC-rich and the coral framestone shows aragonite- rich carbonate mineralogies. Detailed elemental compositional studies suggest precipitation and filling mechanisms of clay-size lime muds in bored void space. Multiple boring of limestones and corals by boring organisms may produce several isolated void spaces that become filled with seawater, and authigenic clay-size crystals of HMC-rich carbonates may precipitate in the bored void space and fill the void space. The HMC-rich and clay-size carbonates eroded from the lime-mud borings may be important sources for the fine fraction of lime mud in the coral reef basins.
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CARBON ISOTOPE FLUCTUATIONS THROUGH THE NEOPROTEROZOIC-LOWER CAMBRIAN BIRMANIA BASIN, RAJASTHAN, INDIA
Anil Maheshwari, aA.N. Sial, and bS.C. Mathur
Dept. of Geology, University of Rajasthan, Jaipur-4, India; [email protected]
aNEG-LABISE, Dept. of Geology, C.P. 7852, Federal University of Pernambuco, Recife, Brazil-50,732-970
bDept. of Geology, J.N.V. University, Jodhpur, India
ABSTRACT: The results of a carbon isotope study from a hitherto unexplored marine sediments from the Birmania basin, Northwestern India are reported, which documents significant isotope variation across the Precambrian-Cambrian boundary (Pc/C). An attempt has been made to identify carbon isotope chronostratigraphic marker for the Precambrian-Cambrian boundary in the sedimentay succession. The transition is marked by a negative excursion during phosphoritic activity at the base of the Birmania succession which is followed by a positive excursion close to the boundary and a swing back to less positive values in the Early Cambrian. The characteristics of the paleoenvironment during the transition interval is also discussed.
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BIOFACIES AND SEQUENCE STRATIGRAPHY OF THE EOCENE SUCCESSION, AT HAMZEH-ALI AREA, NORTH-CENTRAL ZAGROS, IRAN
H.V. Moghaddam, A. Seyrafian, and P. Taraneh
Geology Department, Faculty of Sciences, University of Esfahan, Esfahan 81744, Iran
ABSTRACT: The predominant biofacies of Eocene deposits at the Hamzeh-Ali area in highlands of Zagros Mountains are: (1) planktonic foraminifera, (2) nummulitid-discocylinid-planktonic foraminifera (3) nummulitid-discocyclinid, (4) Alveolina-Nummulites, (5) Alveolina-Orbitolites-Somalina, and (6) Alveolina-miliolids-bioclasts.
Palaeoecology and sedimentary environments in association with the occurrence of foraminifera suggests an open shelf of carbonate platforms (with ineffective barrier) with emphasize on deep shelf and inner to outer shallow shelf of an open-marine environment were present at the study area during the Eocene.
Three depositional sequences were also recognized in the Eocene succession. Transgressive Systems Tracts are characterized by the occurrence of larger and flat perforated and planktonic forams. Abundance of imperforated forams and presence of smaller perforated forams are associated with Highstand Systems Tracts. Sequence boundaries are characterized by abrupt change in lithology and faunal succession.
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EVAPORITES IN ALBANIA AND THEIR IMPACT ON THE THRUSTING PROCESSES
Telo Velaj
1700 Street Rd., Apt. S-4, Warrington, PA 18976; [email protected]
ABSTRACT: The Upper Triassic evaporites are widespread in Albania, Greece, and Montenegro (mainly on External zones). They belong to the Alpine orogene system of the Periadriatic chains. The Upper Triassic age of the evaporites up to date had been determined by spore-pollen examinations only for the Ionian zone. For the Kruja and Korabi zones there are no determinations. All the evaporite outcrops in the Ionian zone (Dumrea's, Glina's Zavrohona's, Delvina's, Picar-Kardhiqi's, Bashaj's, Xara's, Filat's etc) result from eruption under the effect of thrust tectonics. The wells drilled both in Albania and Greece have shown a wide extension of the evaporites on the surface. The evaporite outcrops are absent in the Kruja zone in Albania. Evaporitic diapirs have extruded through the thrusting faults of the zones, belts and units. In some cases they have flowed nearly vertically in the center of the carbonate anticlinal structures. The External zones resulted from the orogenic activity over which evaporites have played a large role with the form of folds and thrust belts. Especially, they have helped the thrusting process of the structural belts and tectonic zones.
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RECENT SEDIMENTS FROM A COASTAL POND, EASTERN MARGIN OF THE DEAD SEA, JORDAN
1Fadhil N. Sadooni, 2Walid Saqqa, and 3Ghada Abrahim
1Department of Geology, United Arab Emirates University, PO Box 17551, Al-Ain, United Arab Emirates
2Department of Earth & Environmental Sciences, Yarmouk University, Irbid, Jordan
3Department of Geology, University of Auckland, Private Bag 2309, Auckland, New Zealand
ABSTRACT: A marginal pond on the eastern coast of the southern part of the Dead Sea in Jordan receives fresh and thermal waters from adjacent areas. The pool has a narrow "intertidal" zone in which halite-encrusted stromatolites flourish. The muddy sediments of the pool consist of a mixture of detrital clay minerals and calcite with authigenic halite and dolomite. The association of halite with dolomite supports the assertion that dolomite is an evaporitic mineral. The absence of gypsum in these sediments is attributed to bacterial reduction of sulfates.
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Copyright 2002 Northeastern Science Foundation